With the recent spread and progress of appliances such as a cell phone, a higher capacity battery as a power source has been asked for. In such situation, a metal air battery has drawn attention as a high capacity battery superior to a lithium-ion battery which is currently used generally, since an oxidation-reduction reaction of the oxygen is performed at a positive electrode (air electrode) by utilizing oxygen in the air as an active material for the positive electrode, and an oxidation-reduction reaction of a metal constituting a negative electrode is performed at the negative electrode, so that charging and discharging are possible allowing high energy density (Non Patent Literature 1).
However, there remain drawbacks to be overcome in a metal air battery. For example, it has been proposed that high surface area SiO2 should be mixed into a positive electrode material so as to improve capacity or coulombic efficiency (Patent Literature 1).